Specific inhibitors of tyrosine-specific protein kinase, synthetic 4-hydroxycinnamamide derivatives

Several newly synthesized 4-hydroxycinnamamide derivatives such as 3-(3',5'-di-isopropyl-4'-hydroxybenzylidene)-2-oxindol (ST 280), 3-(3',5'-di-methylthiomethyl-4'-hydroxybenzylidene)-2-oxindole (ST 458), alpha-cyano-3-ethoxy-4-hydroxy-5-phenylthiomethylcinnamamide (ST 638) and 3-(3'-ethoxy-4'-hydroxy-5'-phenylthiomethylbenzylidene)-2-pyrol idinone (ST 642) were found to inhibit tyrosine-specific protein kinase activity of the epidermal growth factor (EGF) receptor with IC50 values of 0.44 microM, 0.44 microM, 0.37 microM and 0.85 microM, respectively. None of them showed inhibitory effect on the enzyme activities of serine- and/or threonine-specific protein kinases such as cAMP-dependent protein kinase, Ca2+/phospholipid-dependent protein kinase C, casein kinase I and casein kinase II. In addition, none of them had effect on Na+/K+-ATPase or 5'-nucleotidase. The results suggest that the compound ST 280, ST 458, ST 638 and ST 642 are potent and specific inhibitors of tyrosine-specific protein kinase.